1. Field of the Invention
The present invention relates to an optical system for photographing a stereoscopic image and a stereoscopic image photographing apparatus having the optical system, which are particularly arranged to be capable of varying magnification and are adapted to obtain images having parallax for right and left eyes (parallactic images) including a photographing range of a relatively wide angle of view.
2. Description of Related Art
In order to observe a stereoscopic image, it is necessary to produce a plurality of parallactic images. Heretofore, there have been proposed a variety of stereoscopic image photographing optical apparatuses or stereoscopic image photographing optical systems for obtaining a plurality of parallactic images, for example, in Japanese Laid-Open Patent Application No. Hei 8-251624, Japanese Laid-Open Patent Application No. Hei 8-307904, etc.
In the case of an embodiment shown in FIG. 1 set forth in the above Japanese Laid-Open Patent Application No. Hei 8-251624, the stereoscopic image photographing optical system is constructed with two, right and left, variable-reflection-angle mirrors, two, right and left, mirrors, two, right and left, pairs of polarizing filters, two, right and left, lens systems, and one image sensor. Then, the pair of polarizing filters are rotated to change the amounts of light based on right and left parallactic images, so that light beams passing respectively through optical paths for the right and left parallactic images are alternately led to the image sensor, thereby obtaining the parallactic images at the image sensor.
Further, in the case of an embodiment shown in FIG. 2 set forth in the above Japanese Laid-Open Patent Application No. Hei 8-251624, the stereoscopic image photographing optical system is constructed with two, right and left, variable-reflection-angle mirrors, two, right and left, mirrors, a polarizing beam splitter, a polarizing filter, a lens system, and an image sensor.
Then, similarly to the embodiment shown in the above-mentioned FIG. 1, the polarizing filter is rotated to change the amounts of light based on right and left parallactic images, so that light beams passing respectively through optical paths for the right and left parallactic images are alternately led to the image sensor, thereby obtaining the parallactic images at the image sensor.
In the case of Japanese Laid-Open Patent Application No. Hei 8-307904, the stereoscopic image photographing optical system is constructed with two, right and left, objective lenses, two, right and left, shutters, a half-mirror for combining two, right and left, images, and a variable magnification optical system for re-forming, on the image sensor, images formed on primary image forming planes of the two, right and left, objective lenses.
However, the stereoscopic image photographing optical system disclosed in the embodiment shown in FIG. 1 set forth in the above Japanese Laid-Open Patent Application No. Hei 8-251624 has such a drawback that, since two photographic lenses are used for one image sensor, optical axes of the photographic lenses inevitably lean with respect to the image sensor, thereby causing blurring at a marginal portion of an image plane.
Further, in the stereoscopic image photographing optical system disclosed in the embodiment shown in FIG. 2 set forth in the above Japanese Laid-Open Patent Application No. Hei 8-251624, the polarizing beam splitter, which is used as an optical-path combining element for combining two optical paths, is composed of a multiple layer. Therefore, there is such a drawback that the characteristics of spectral reflectance are caused to change by a change in angle of incidence of a light flux, thereby causing color unevenness in an image plane.
Further, in the stereoscopic image photographing optical system disclosed in the above Japanese Laid-Open Patent Application No. Hei 8-307904, there is such a drawback that, since aerial images formed by the two, right and left, objective lenses are re-formed by a relay lens, the number of constituent lens elements of the entire optical system becomes large, thereby complicating the construction of the whole apparatus.
In addition, there is such a problem that, since the right and left optical paths are combined by the half-mirror, each of the optical paths comes to have an amount of light decreased due to the reflection and transmission at the half-mirror.